The present invention pertains to radar systems, and in particular, synthetic aperture radar (SAR), and in one aspect, to the generation of images with bistatic SAR.
Bistatic SAR is a process of generating an image of the reflected electromagnetic energy from the surface of the earth by combining the magnitude and phase measurements of many spatially distributed locations of an illuminator and/or a receiver. In bistatic SAR, measurements are generally compensated for illuminator location and motion, reflective surface location, and receiver location and motion. Phase compensation is generally performed for each fast-time and slow-time sampling of the measured signals. The phase compensation coefficients can be determined accurately when the location and motion of the illuminator and receiver are accurately known. Unlike monostatic SAR where the illuminator and receiver are co-located, this information is difficult to accurately obtain in bistatic SAR making it difficult to align the two separate reference systems of a bistatic SAR system. As a result, the generation of quality images in a bistatic SAR is difficult.
Conventional bistatic SAR imaging systems have used a data-link between the illuminator and receiver to communicate the location and motion information. This approach increases the complexity of such systems and furthermore, has several inherent difficulties and risks. For example, maintaining a data link in a real-time operational environment may be difficult due to interfering and jamming signals resulting in an inability to generate a quality image. It may also give away the location of the illuminator or receiver and may require that the receiver and illuminator be within line-of-site depending on the frequency.
Thus there is a general need for an improved method and system for generating of a bistatic SAR image. There is also a need for a method and system for generating a bistatic SAR image without a data-link to convey positional information between the illuminator and the receiver. There is also a need for a method and system for generating a bistatic SAR image without knowledge of the illuminator""s position and heading. There is also a need for a method and system for generating a bistatic SAR image without alignment of the receiver and illuminator.